Screens, particularly for wood chips



Dec. 17, 1968 J. LARSSON v 3,4l6,660

SCREENS. PARTICULARLY FOR WOOD CHIPS Filed Sept. 2, 1966 6 Sheets-Sheet 1 L u I FIGJ T +4;

Dec. 17, 1968 J. LARSSON SCREENS. PARTICULARLY FOR WOOD CHIPS 6 Sheets-Sheet 2 Filed Sept. 2, 1966 Dec. 17, 1968 J. LARSSON & 5

SCREENS. PARTICULARLY FOR WOOD CHIPS Filed Sept. 2, 1966 i 6 Shets-Sheet 5 D c. 17,1968 I .LLARSSON 3,416,66o

SCREEN& PARTICULARLY FOR WOOD CHIPS Filed Sept. 2, 1966 6 Sheets-Sheet 4 FGJ.

Dec. 17, 1968 J. LARssoN 5 5 SCREENS. PARTICULARLY FOR woon CHIPS Filed Sept. 2, 1966 6 Sheets-Sheet 5 J. LARSSON Dec. 17, 1968 I SCREENS PARTICULARLY FOR WOOD CHIPS 6 Sheets-Sheet 6 Filed Sept.

United States Patent ABSTRACT OF THE DISCLOSURE Screening apparatus having a casing flexibly Suspended from an overhead support and supporting a plurality of removable screen sections arranged in annular array. A motor with an eccentrc mass distribution is supported in the casing for producing a generally planar vibratory motion of the screen while the 'latter is retained against rotary motion.

This invention relates to a screen particularly adapted for screening wood chips. The screening is efiected by substantially planar shaking motions of a non-rotary screen plate or plates, and the material to be screened preferably is supplied to the screen substantally centrally. Screens of this type usually are called sh aker screens.

The invention has 'for its object to increase the capacity and effectiveness of such screens to a substantial degree. A further object of the inventon is to produce a screen which is easier to-operate and maintain and also to lengthen its life. Another object of the invention is to facilitate the cleaning and replacement of the screen members which may consist of screen plates, 'a wire network or wire cloth, etc. A still further object of the invention is to render it possible a simple manner to adjust the shaking or vibratory movement to the nature of the material to be screened, and to give the screen a compact design. According to the invention, the drive efiect required and, thus, the manufacturing costs -as well as the operation costs of the screen can be reduced.

`In accordance with the invention there is provided screening apparatus which comprises a casing of bowlshape, which is resiliently suspended from an overhead support by suitable means such as cables or the like. A removable screen is mounted in the casing, the screen including a plurality of individually removable screen sections arranged in an annular array. A drive means is supported in the casing for producing a generally planar 'vibratory motion of the screen While the latter is retained against rotary motion.

One embodinent-mot restricting the scope of the invention-is shown on the accompanying drawings wherei FIGURE 1 shows a side View of a screen according through one of the doors for the mounting and removal of the screen plates.

'In FIGS. 5 and 6 as well as FIGS. 7 and 8 the same scale was used, the remaining figures being drawn on different Scales.

Referring now to F IG. 1 of the drawings, 1 designates a cyclone Separator with an inlet 2 for Wood chips supplied from a chopper, and an outlet 3 for the conveying air. .The Separator is supported on a frame 4 and provided With an outlet 5 from` which the chip material is discharged centrally onto a shaker or swinging screen. The latter is shaped as a bowl 6 and Suspended on flexible members, preferably cables (wires) 7 extending between lugs 8 on the screen and uprights or standards 9. Preferably four of such uprights are provided.

The supplied chips fall onto a top cone or hood 10.

Reference is now made mainly to FIGS. 2 and 3. In the screen (bowl) 6, below the detachable top cone 10, an electromotor 11 is mounted on a bottom plate 12 and enclosed in a central cylinder 13 covered by the cone 10. Walls or part-itions 14 extendng radially from the central sha'ft formed by the portions 12 and 13 divide the screen into a plurality of sections (sectors), in the embodiment shown eight in number. In a horizontal View, the screen preferably has the shape of a regular polygon (see FIG. 2). 'I he partitons 14 are Secured to the enclosing boWl-*sh-aped outer wall 6.

Where necessary, reinfo rcements of a suitable design are provided for, such as the angle irons shown in FIGS. 3 and 4.

The partitons 14 are shown in a greater detail also in FIG. 4. On said partitions support bars 15 a-re mounted for carrying guide plates 16 which pre'ferably are unperforated and curved downwards at their outer ends. The enclosing frame plate or bowl 6 projects upwards above the outer ends of the 'guide plates 16. Thus, at varying Operating conditions (due, for example, to variable supply or varying composition of the 'material to be screened) a ring or dam o f material to be screened can be built up temporarily at the circumference.

The partitions 14, frrthermore, are provided with inclined chutes 17 and 18 respectively, into which' coarse screen plates 19 and fine screen plates 20, respectively, are inserted.

The sad partitions also include upper recesses 21 and lower recesses 22.

The lower inner ends of the plates 19 for coarse screening are arranged about a 'central discharge funnel 23 for the splinters which do not pass through said plates. In an analogo-us manner, the plates 20 for fine screening are connected with their lower inner ends to a lower central discharge funnel 24 for the chips passing through the coarse screen 19 but not through the' fine screen 20. These latter chips fall down onto a conveyor 25 for their further transport to a bin (and from there to the digesters).

The material (chips) passing through the fine screen plates 20 falls onto a funnel-shaped bottom 26' On which it slides downwards to a helical chute 27. This chute which is shown in detail in FIGS. 5 and 6 is provided on one side with an outlet 28.

At the upper edges of the bottom 26, doors 29 are provided, one for every sector, see particularly FIGS. 7 and 8. The doors 29 can be removed after their respective handles 30 have been turned and disengaged from a corresponding stop on the screen frame (for example on the partitions 14). After the doors have been removed, the screen plates 19, 20 can be inserted into or removed from the chutes 17 and 18 respectively (or are easily accessible for cleaning and clearing). On doors 29, springs 31 are mounted by clamping members 32 which permit the spring to rock to some extent, in such a manner, that the spring presses the screen plates 19, 20 uniformly into their positions when the door is being closed.

The shaft 33 of the motor 11 (FIG. 3) is mounted in the center of the screen. On said shaft an arm 34 is secured, to which arm a variable number of weights 35 can be secured. At its outer end the arm 34 carries a member 36 of angle or U-shaped, one fiange of which extends into a circular U-beam 37 mounted on the bottom 12 and adapted to prevent separation of the weights if they should loosen.

The electric current is supplied to the motor 11 through a cable in the pipe 38 (FIG. 2).

The described apparatus operates as follows. The material to be screened (chip material) falls from the outlet 5 onto the cone and from there onto the guide plates 16.

The weights 35 cause the motor shaft 33 to assume a position somewhat oblique in relation to the vertical, so that the entire screen (in its statonary position) is somewhat inclined. When the motor is started, the rotating arm 34 with the weights 35 imparts to the screen a substantially horizontal and plane shaking motion (a circular swinging motion). As a result thereof, the screen tilts, but its does not rotate. The amplitude of vibration is determined by the size of the weights 35 and can be Varied by changing the same.

Due to the said shaking motion, the chip material falling down centrally onto the cone 10 is moved outwards onto the guide plates 16 and falls down onto the coarse screen plates 19 all around the periphery (perimeter) of the screen. The coarse splinters which do not pass through the said plates, are moved by the shaking motion downwards and inwards on the plates and fall down into the funnel 23 from where they are removed from the screen.

The Wood chips of the size suitable for the digester pass through the coarse screen plates 19 and are moved by the shaking motion downwards and inwards to the funnel 24 onto the conveyor 25 for further transport (to a digeste').

The smallest chips, i.e. the finest f'action of the material, pass through the fine screen plates 20 down onto the bottom 26 by which they are shaked into the chute 27 and leave the screen through the outlet 28.

Due to the sweeping motion of the arm 34 with the weights 35 through the openings 21, the bulky and spreading splinters are prevented from accumulating on the coarse screen plates 19. By the said sweeping motion, the

splinter heaps on the coarse screen plates 19 are directly broken up, and the splinters are thrown into adjacent sectors. In this way `a more uniform distribution is obtained. The air draught effected by the arm (with the weights) also contributes to preventing the clogging of the coarse screen plates by the spreading splinters, which clogging is a troublesome phenomenon in conventional chip screens.

Due to the openings 22, the screened chps can accumulate temporarily on the lower portion of the fine screen plates 20 about the funnel 24, if the supply is not uniform.

Due to the fact that, according to the invention, a plurality of screens in a circular arrangement are assembled to a compact unit with common drive and common feed (supply), a very high capacity, in combination with great sirnplicity, is achieved. Furthermore, the inspection, cleaning and replacement of the screen plates can be carried out in a very simple manner. The screen, moreover, will operate smoothly and without breaks, even if the supply of material or the nature of the material etc varies. Material accumulated on one screen area will be transferred to an adjacent screen area.

The screen keeps its center of gravity substantially on a vertical (statonary) line, and thus the load on the carrying elements is substantially static.

For supporting the screen, torsion rods or one or more &416560 elastc posts may be used in combination with or instead of the wires 7.

The apparatus described and shown may be modified to a certain extent within the scope of the invention.

The motor need not be an electromotor, but it may be, for example, an internal combustion engine, a hydraulic or pneumatic motor.

The motor need not be rigidly connected with the screen, but it may be of the statonary type and drive the screen via an eccentric device. Irrespective of whether t e motor is of the statonary type or rigidly connected with the screen, it is not necessary that the distribution of weight for elfecting the shaking motion be eccentric because the motor shaft itself may be eccentric or have attached weights or the like for attaining an eccentric distributionof weight, i.e. a Weight distribution which is asymmetrical in relation to its geometrical axis. The shaft, instead, may be fully symmetric and form a non-rotary stator, about which a driven rotor with asymmetric weight distribution rotates.

In certain cases it may be suitable to control the screen motions in the vertical direction by springs or like elastic elements, particularly when the wires 7 are replaced by or associated with torsion rods or the like.

The arm 34 need not be weight-loaded. It may be replaced by a double-arm balanced about the shaft 33 and having as its only object to sweep over the screen plates and thereby to distribute the material to be screened.

What I claim is:

1. Screening apparatus comprising a casing of bowl shape, means resiliently suspending the casing from an overhead support, a removable screen mounted in said casing, said screen including a plurality of individually removable screen sections arranged in an annular array, and means in said casing for producing a generally planar vibratory motion of the screen while the screen is retained against rotary motion.

2. Screening apparatus as claimed in claim 1, wherein said means for producing vibratory motion of the screen comprises a motor centrally positoned in said casing, and an eccentric distribution of weight coupled to said motor for being driven thereby in a plane to produce the planar vibratory motion of the screen.

3. Screen apparatus as claimed in claim 1, wherein said screen sections are inclined downwardly and inwardly towards the center of the screen, said screen sections defining a central opening for the outlet of screened material remaining on the sections.

4. Screen apparatus as claimed in claim 1, comprising a plurality of radial partitions in said casing separating said screen sections and extending thereabove.

5. Screen apparatus as claimed in claim 4, comprising distribution members supported by said partitions at a level above said screen for receivin material to be screened, said distribution members being inclined downwardly in a direction radially outwards of the center of the casing to feed the material to be screened to the screen sections at the peripheries thereof.

6. Screen apparatus as claimed in claim 5, comprising a second removable screen constituted by a plurality of screen sections in annular array, the second screen being interposed between the first said screen and the bottom of the casing.

7. Screen apparatus as claimed in claim 4, wherein said partitions have openings permitting transfer of material to be screened from one section to an adjacent section;

8. Screen apparatus as claimed in claim 7, wherein said motor has a shaft and a member eccentrically secured thereto which travels through the openings in said partition as the shaft rotates.

9. Screen apparatus as claimed in claim 8, wherein said casng has a funnel-shaped bottom beneath the screen sections for receiving material passing therethrough, said bottom having an outlet for the material thereon.

(References on following page) Barker 209-275 X Fuchs 209-275 Bunge 209-332 X White 209-332 Miller et al 209-332 Halsey 209-405 Prescott 209-363 X 6 FOREIGN PATENTS 436,518 3/1912 France.

TIM R. MILES, Assistant Examner.

FRANK W. LUTTER, Pr'ma'y Exam'ner. 

